Fabrication of metal shapes



te r

This invention relates to the fabricating of shapes of pure refractorymaterials of predetermined composition.

Briefly according to the invention, there is provided a process ofmaking shapes of desired contour of relatively pure refractory material,which comprises depositing selected material on a suitable mastersupport by heating and accelerating particles of such material in astream of selected gas flowing through an electric arc of the generaltype disclosed by Gage Patent No. 2,806,124, while maintaining thetemperature of such master below its melting point. The resultingdeposited layer has a characteristic microstructure in which microscopiclamellules or leaves of irregular shape are inter-locked one withanother. The master and deposited layer are then separated from eachother, providing a shape thereof having the desired contour andcomposition.

Tungsten tubes and other shapes are readily fabricated according to thisinvention by coating tungsten metal onto a pattern and then separatingthe pattern from the coating. Shapes of other refractory metals, such asmolybdenum, niobium, chromium, tantalum, nickel, zirconium, andtitanium, as well as compounds and mixtures thereof, can also befabricated in this fashion.

Industry has need for refractory metals in various shapes. In particulartungsten metal is desired as rela tively sin-all hollow bodies for useas electron emitters in vacuum tubes in the radio and television field.Prior art tungsten electron emitters were fabricated with greatdifiiculty, for example, by swaging or by wrapping tungsten :ire arounda pattern of the desired shape and then fusing in position. Such methodswere all time-consuming and costly.

Tungsten carbide and similar refractory materials have been previouslyprepared in intricate shapes as dies by means of the detonation coatingprocess covered in US. Patent No. 2,714,563. In such fabrication processof dies, which is covered in my copending application, Serial No.648,265, filed March 25, 1957, now Patent No. 3,048,- 060, which is acontinuation-in-part of my now abandoned application Serial Number377,030, filed August 28, 1953, a refractory material is coated onto thesurface of a pattern. The coating is then covered by a substantial layerof supporting metal. The pattern is then removed to form a metal basecontaining an inner liner of refractory material. Such prior art processcannot be employed to fabricate tungsten or other pure metal shapessince the detonation reaction used in such process incorporates somecarbon, carbides and/or foreign oxides in the final product coating.

1 have found that a high-pressure arc coating process can be employed toproduce adherent, dense, non-porous coatings of pure tungsten metal. Nocontaminants, such as carbides and foreign oxides, are present in thecoating since inert gases, such as argon, helium, nitrogen, andhydrogen, are usually employed to protect the refractory metal duringthe coating process.

This novel process for preparing refractory metal shapes 3,3253%Patented Mar. 26, T963 comprises the steps of forming a pattern ormaster body having the desired shape of the finished product, depositinga coating of refractory metal or mixture thereof of desired thicknessonto the pattern by means of the highpressure are torch process ofPatent No. 3,016,447 and then separating the pattern from the coatedshape.

The method of removal of the pattern after the coating step is completedepends upon the nature of the pattern. If it is aluminum, for example,it can be dissolved in sodium hydroxide solution. If it is brass, forexample, it can be dissolved in nitric acid. A pattern of low meltingpoint material can be easily removed by heating without affecting thesolid coating. The pattern can also be formed of easily deformablematerial which can be forced from the refractory metal shape bymechanical means. The master material might also be removed physicallyby machining methods.

The following example of the fabrication of a tungsten metal shape isillustrative of the process. An aluminum tube inch O.D., inch I.D., and1% inches long was plated with a 0.010 inch thick coating of tungstenmetal by means of the non-transferred arc torch process. The torch wasoperated by striking an arc of 45 volts (D.C.S.P.) and amps. between aninner stick electrode and a nozzle electrode with c.f.h. argon gaspassing through the /8 inch LD. torch nozzle. The tungsten powder passeddown through the arc and out through the nozzle. The aluminum tube wasrotated and traversed under the torch outlet which was maintained /8inch from the aluminum tube. The resulting aluminum body coated withtungsten was placed in a 30 weight percent aqueous sodium hydroxidesolution for about 4 hours. After this time the aluminum was completelydissolved. The remaining tungsten tube was 0.395 inch 0.1)., 0.375 inchLD. and 1% inches long.

The above example employed the non-transferred arc torch coatingprocess. The transferred arc torch process wherein the support is in thearc circuit could also be used provided an electrical conductor isemployed as the pattern material.

This process has been employed to form hollow shapes of tungsten. Theprocess is equally applicable to other refractory metals such aschromium, niobium, molybdenum, nickel, tantalum titanium, and zirconium,as well as to mixtures of refractory metals with emissive materials,such as the emissive metal oxides thoria or yttria, for example. In thelatter case the present invention has a decided advantage over prior artmethods. Pure tungsten can be shaped with difficulty into some forms byswaging, drawing and pressing which require some ductility in the metal.Tungsten-thoria mixtures on the other hand, are quite brittle and arealmost impossible to fabricate in diverse shapes. This process isapplicable to fabricating shaped of almost any refractory material whichwould be too brittle to Work into shape. Laminated articles can befabricated according to the invention by coating alternate layers ofmetal and compounds, such as emissive material, onto a pattern and thenremoving the pattern. 1

What is claimed is:

1. Process of making metal shapes of selected refractory material, whichcomprises applying refractory material selected from the classconsisting of refractory metals such as tungsten, chromium, niobium,molybdenum, nickel, tantalum, titanium, and zirconium, as well asmixtures of refractory metals with emissive materials, such as theemissive metal oxides thoria or yttria to a temporary solid support byan electric arc-gas process which heats and accelerates particles ofsaid selected refractory material in an arc efiluent of inert gas toform a chemically unchanged coating of such selected material of desiredshape on such support below the melting temperature of the latter toprevent intermingling, and then separating such coating and such supportwithout changing such shape.

2. Method of fabricating articles having internal surfaces of desiredpredetermined contour and of a predetermined material composition, whichcomprises providing a temporary solid master having an external surfacecomplimentary in contour to said internal surface, providing a highthermal content effluent comprising a stream of selected gas heated by ahigh pressure are; feeding to said eflluent at a controlled rate amaterial of composition selected from the class consisting of refractorymetals such as tungsten, chromium, niobium, molybdenum, nickel,tantalum, titanium, and zirconium, as well as mixtures of refractorymetals with emissive materials such as the emissive metal oxides thoriaor yttria which, when deposited on the master, forms a built up layer ofsaid predetermined material composition, directing the resulting streamof material composition bearing effluent against the external surface ofsaid temporary master until a built up chemically unaltered layer ofsaid predetermined material composition of desired thickness is formedbelow the melting temperature of the master to prevent intermingling,and then removing said master to provide said article.

3. Process of making shapes of refractory metal, which comprisesdepositing refractory metal selected from the class consisting ofmolybdenum, niobium, chromium, tantalum, nickel, zirconium, andtitanium, as well as compounds and mixtures thereof on a suitable solidsupporting member by electric arc heating while maintaining thetemperature of such supporting member below its melting point to preventintermingling, and then removing the resulting shape composed of suchrefractory metal chemically unaltered from such supporting member.

4. Process of making desired shapes of tungsten metal, which compriseselectric arc welding together particles of such metal on a temporarysolid support of brass under a stream of inert gas selected from theclass consisting of argon, helium, nitrogen and mixtures of argon andnitrogen, without melting said brass support to prevent interminglingand then separating the resulting shape of tungsten from such brasssupport by dissolving the latter in acid.

5. The method of making shapes of relatively pure material selected fromthe class consisting of niobium, chromium, molybdenum, nickel, tantalum,titanium, tungsten, zirconium and compounds and mixtures thereof, whichcomprises discharging a stream of selected inert gas against a localarea of the surface of a temporary solid supporting member, drawing ahigh-pressure are between a nonconsurnable electrode and an annularnozzle, feeding and accelerating particles of powdered material selectedfrom such class with such gas stream through said arc, heating suchparticles of powdered material in said arc, depositing and weldingtogether the so heated particles of material on said local area asinterlocking microscopic leaves of irregular shape built up, to athickness that is self-supporting when said temporary supporting memberis separated therefrom, producing relative movement between said memberand said inert gas stream and powdered material feed heated by anelectric are, so that the shape of such welded deposit of selectedmaterial corresponds to that of the surface of said supporting member;said deposition and welding being carried out below the meltingtemperature of said supporting member to prevent intermingling and thenseparating the resulting so deposited are welded shape of selectedmaterial and said temporary supporting member from each other.

6. Process of fabricating members of pure refractory metal selected fromthe class consisting of molybdenum, niobium, chromium, tantalum, nickel,zirconium, and titanium, as well as compounds and mixtures thereof whichcomprises discharging a stream of inert gas from an electric arc torchprovided with a non-consumable central electrode surrounded by anon-consumable annular electrode constituting the nozzle of such torch,establishing an electric are between such electrodes, feeding acontrolled flow of refractory metal particles into such gas stream fordischarge from said nozzle with such are heating said gas stream andrefractory metal particles, applying the resulting hot efliuentcontaining such gas and such heated and accelerated refractory metalparticlesto a local surface area of a solid support composed of materialthat can be removed by a chemical which does not remove the refractorymetal, thereby depositing on such local surface area of the support alayer of welded microscopic lamellules of refractory metal particles,and relatively moving such effluent and support so as to coat a desiredarea of the support, such coating being accomplished below the meltingtemperature of the surface of said support to prevent intermingling andthen removing the support by a suitable chemical, leaving the desiredmember composed of such pure refractory metal.

7. Process of fabricating electronic members composed of refractorymetal selected from the class consisting of molybdenum, niobium,chromium, tantalum, nickel, zirconium, and titanium, as well ascompounds and mixtures thereof and emissive material selected from theclass consisting of thoria and yttria, which comprises simultaneouslydischarging a stream of inert gas and a mixture of refractory metal andemissive material particles as an extremely hot etlluent from anelectric arc torch in which a high pressure arc is drawn between the endof a central electrode and a nozzle electrode surrounding such centralelectrode applying such eiiluent to a solid support until there is builtup thereon without intermingling therewith a composite composed ofmicroscopic lamellules of such particles that are interlocking andwelded one to another without any change in the original purity of therefractory metal and emissive material constituting such particles, andsubsequently removing said support from said composite which thereuponconstitutes the electronic member.

8. The process of fabricating electronic members which comprisesdepositing alternate layers of refractory metal selected from the classconsisting of molybdenum, niobium, chromium, tantalum, nickel,zirconium, and titanium, as well as compounds and mixtures thereof andemissive material selected from the class consisting of thoria andyttria to a suitable solid support by alternately applying theretowithout melting said support an extremely hot effluent comprising aninert gas stream and refractory metal particles, heated by an electricarc; and an extremely hot eilluent comprising an inert gas stream andemissive material particles heated by an electric arc; and subsequentlyremoving said support from the resulting composite of alternating layersof refractory metal and emissive material which composite thereuponconstitutes the electronic member.

9. Process of fabricating shapes of refractory material selected fromthe class consisting of refractory metals such as tungsten, chromium,niobium, molybdenum, nickel, tantalum, titanium, and zirconium, as Wellas mixtures of refractory metals with emissive materials, such as theemissive metal oxides thoria or ytrria which comprises simultaneouslydischarging a stream of inert gas, a high pressure are and refractorymaterial particles as an extremely hot efiiuent from an electric arctorch in which such high pressure arc is drawn between the end of atorch electrode and a solid support, applying such effluent to suchsupport until there is built up thereon without 5 interminglingtherewith a composite composed of micro scopic lamellules of suchparticles that are interlocking and welded one to another without anychange in the original purity of the refractory material constitutingsuch particles, and subsequently removing said support from saidcomposite.

References Cited in the file of this patent UNITED STATES PATENTS 6Hopkins Feb. 27, 1940 Strossel Apr. 28, 1942 Strossel Apr. 28, 1942Aicher July 18, 1944 Lambert Nov. 22, 1949 Shepard Mar. 11, 1952. HuggerMar. 3, 1953 Townsend May 15, 1956 Gfeller July 10, 1956 Gage Sept. 10,1957 Rhodes Feb. 25, 1958 Kelley June 10, 1958 Ekkers May 19, 1959

1. PROCESS OF MAKING METAL SHAPES OF SELECTED REFRACTORY MATERIAL, WHICHCOMPRISES APPLYING REFRACTORY MATERIAL SELECTED FROM THE CLASSCONSISTING OF REFRACTORY METALS SUCH AS TUNGSTEN, CHROMIUM, NIOBIUM,MOLYBDENUM, NICKEL, TANTALUM, TITANIUM, AND ZIRCONIUM, AS WELL ASMIXTURES OF REFRACTORY METALS WITH EMISSIVE MATERIALS, SUCH AS THEEMISSIVE METAL OXIDES THORIA OR YTTRIA TO A TEMPORARY SOLID SUPPORT BYAN ELECTRIC ARC-GAS PROCESS WHICH HEATS AND ACCELERATES PARTICLES OFSAID SELECTED REFRACTORY MATERIAL IN AN ARC EFFLUENT OF INERT GAS TOFORM A CHEMICALLY UNCHANGED COATING OF SUCH SELECTED MATERIAL OF DEISREDSHAPE ON SUCH SUPPORT BELOW THE MELTING TEMPERATURE OF THE LATTER TOPREVENT INTERMINGLING, AND THEN SEPARATING SUCH COATING AND SUCH SUPPORTWITHOUT CHANGING SUCH SHAPE.